I am a 28-year-old male. I have two paternal grandparents who died of cancer ( one, with colon cancer). My father, his brother and my older brother have all had colon cancer. My great-grandmother died of cancer. I have never been tested for colon cancer before. My family is pushing me to be tested. Should I be tested? I have had no symptoms as of yet.
Colon cancer, which includes cancer of the rectum, is the second leading cause of cancer deaths in the U. S., exceeded only by lung cancer. No single cause of this cancer is known, although epidemiological studies have identified some dietary factors that may play a role, and studies of families in which colon cancer has occurred frequently have provided some clues to the genetics of the disease.
Colon cancer is believed to develop from benign polyps of the colon of the type called adenomatous polyps. These are found in more than 30 percent of people over 50, and are more common with age. They grow slowly, and the few that become cancerous generally make that transformation after about 5 years. Therefore, colonoscopy to find and remove polyps from someone who has been found to have one need be repeated only about every 3 years. People who have had a colonoscopy which revealed no polyps can probably go 5 to 10 years before being checked again. Doing colonoscopies routinely in people with no symptoms who are not members of families with colon cancer is still controversial, although it is becoming more common.
The fiber content of our diet has long been thought to play a role in colon cancer, but this connection did not appear in a recent analysis of a very large ongoing study of nurses. What did appear in that study and others to be positively associated with colon cancer was intake of animal or saturated fats. Vegetable oils, which are mostly not saturated, showed no association with the disease. Since a large intake of saturated fats, found mostly in meat and dairy products, also is associated with high cholesterol, the connection to colon cancer provides yet another reason to eat a prudent diet low in such fats. Eating cruciferous vegetables — broccoli, brussel sprouts and cabbage — reduces risk, as does taking calcium supplements, aspirin, and other non-steroidal anti-inflammatory drugs. There is suggestive evidence that cigarette smoking increases risk, and that taking hormone replacement therapy reduces it.
The family described by you almost certainly falls into one of the two recognized familial groups whose members are at much greater risk of developing colon cancer than the general population. These two are families with familial polyposis, a dominantly inherited condition in which affected people develop literally thousands of adenomatous polyps throughout the entire bowel, and families with hereditary nonpolyposis colorectal cancer (HNPCC). People with familial polyposis account for about 1 percent of colon cancer cases, whereas people from families with HNPCC account for about 10 percent of all cases.
A family with HNPCC is so defined if there are at least 3 members with colorectal cancer, one of whom is a first degree relative of the other two; in which colon cancer has appeared in at least 2 generations; and in at least one case the disease was diagnosed before the person was 50 years old. Parents and children are first degree relatives of each other; therefore, colon cancer in your paternal grandparent and your father and brother fulfill the first degree relative condition, as well as the multiple generation requirement. We do not know the ages at which they all developed the disease, but since you are 28, and your older brother has been found to have it, I will assume that your older brother was less than 50 years of age when diagnosed. From the facts presented, I could not say whether the family has familial polyposis or HNPCC, but since the former is easily recognized by the pathologist when a cancer is removed, and the latter is much more common, I would assume your family carries HNPCC.
Most colon cancers in members of families with HNPCC develop before the individuals reach age 50. Because of the long lead time between the beginning of an adenomatous polyp and its transformation into colon cancer, polyps are found at colonoscopy in much younger members of such families, and screening family members is recommended starting at age 25. Therefore, you are already somewhat overdue to have a colonoscopy, and I agree with the members of your family who have been urging you to start screening. Colonoscopy is necessary instead of the simpler sigmoidoscopy because in these families many of the cancers arise in the first part of the colon, which cannot be detected by sigmoidoscopy. Members of families with HNPCC also are more likely to get other cancers, particularly ovarian and endometrial cancer in female members. Some experts also suggest routine screening of the women in such families for these two other cancers as well as colon cancer.
Another group known to be at greater risk of developing colon cancer than the general population are people with long standing inflammatory bowel disease (IFB), chronic ulcerative colitis, or Crohn’s disease affecting the colon. Screening such individuals with colonoscopy is also recommended after they have had IFB for 8 to 10 years, the frequency of screening being dependent on how long they have had the disease. If precancerous lesions are found, removal of the entire colon is usually recommended. I doubt if you or other members of your family have IFB, since this is a condition that seldom goes undiagnosed now.